Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $221.44   9.787%   $243.1123   $243.11   $243.10   $243.10  
  Purchase #2 $178.63   8.603%   $193.9975   $194.00   $194.00   $194.00  
  Purchase #3 $133.86   10.698%   $148.1803   $148.18   $148.20   $148.20  
  Purchase #4 $56.28   9.647%   $61.7093   $61.71   $61.70   $61.70  
  Purchase #5 $103.82   13.634%   $117.9748   $117.97   $117.95   $118.00  
  Purchase #6 $234.67   6.182%   $249.1773   $249.18   $249.20   $249.20  
  Purchase #7 $42.53   12.626%   $47.8998   $47.90   $47.90   $47.90  
  7 purchase totals = $971.23       $1,062.0513   $1,062.05   $1,062.05   $1,062.10